A continuing goal of integrated circuit fabrication is to decrease the dimensions thereof. Integrated circuit dimensions can be decreased by reducing the dimensions and spacing of the constituent features or structures. For example, by decreasing the dimensions and spacing of semiconductor features (e.g., storage capacitors, access transistors, access lines) of a memory device, the overall dimensions of the memory device may be decreased while maintaining or increasing the storage capacity of the memory device.
As the dimensions and spacing of semiconductor device features become smaller, conventional lithographic processes for forming the semiconductor device features become increasingly more difficult and expensive to conduct. Therefore, significant challenges are encountered in the fabrication of nanostructures, particularly structures having a feature dimension (e.g., critical dimension) less than a resolution limit of conventional photolithography techniques (currently about 40 nm). It is possible to fabricate semiconductor structures with such feature dimensions using a costly pitch division or double patterning technologies. However, use of such processes is limited because the exposure tools are extremely expensive or extremely slow and, further, may not be amenable to formation of structures having dimensions of less than 20 nm.
The development of new processes, as well as materials useful in such processes, is of increasing importance to make the fabrication of small-scale devices easier, less expensive, and more versatile. One example of a method of fabricating small-scale devices that addresses some of the drawbacks of conventional lithographic techniques is directed self-assembly (DSA) of phase separated block copolymers.
Although DSA block copolymer is useful for fabrication of semiconductor structures having dimensions of less than 40 nm, the self-assembled block copolymer materials are generally restricted to periodic patterns and may not produce nanostructures exhibiting sufficiently low defect levels.
Self-assembled nucleic acids have been investigated for forming semiconductor devices. The specificity of complementary base pairing in nucleic acids provides self-assembled nucleic acids that may be used for self-assembled nucleic acid lithography processes.
U.S. Pat. No. 8,501,923 discloses a self-assembled DNA origami structure. The DNA origami structure is formed from structural units, wherein each structural unit comprises a single stranded polynucleotide scaffold and a plurality of helper/staple strands. The helper/staple strands are designed to be at least partially complementary to the single stranded polynucleotide scaffold such that the helper/staple strands self-anneal with the single stranded polynucleotide scaffold into a structural unit. The DNA origami structure may have dimensions of 100-200 nm with a resolution of 6 nm.
Arbitrary two-dimensional (2D) patterns of self-assembled nucleic acids have been reported in Wei et al., Complex shapes self-assembled from single stranded DNA tiles, Nature, 485 (2012), 623-627. The arbitrary 2D patterns are created using self-assembled DNA molecular canvases that are formed from DNA subunits. The DNA subunit has dimensions of less than 10 nm. The DNA subunit may be a single strand DNA having dimensions of 3 nm. The self-assembled DNA molecular canvas may have dimensions of 200 nm.
Surwade et al. disclose a method of forming custom-shaped inorganic oxide nanostructures by using self-assembled DNA-nanostructure templates. Surwade et al., Nanoscale Growth and Patterning of Inorganic Oxides Using DNA Nanostructure Templates,” J. Am. Chem. Soc., 135 (2013), 6778-6781. The self-assembled DNA nanostructure is deposited on a substrate without registration, and then used as a template for a selective deposition of inorganic oxide material to provide an inorganic oxide nanostructure. The inorganic oxide nanostructure may be used as a hard mask for etching the substrate.
Kershner et al. disclose the placement and orientation of individual self-assembled DNA structures on a lithographically patterned substrate. Kershner et al., Placement and orientation of individual DNA shapes on lithographically patterned surfaces, Nature Nanotechnology, 4 (2009), 557-561. DNA origami, in which a long single strand of DNA is folded into a shape using shorter “staple strands,” is used as the self-assembled DNA structure. Electron beam lithography and dry oxidative etching are used to create DNA origami-shaped binding sites on the materials such as silicon dioxide (SiO2) and diamond-like carbon (DLC).